1. Field of the Invention
This invention permits the very high speed conversion of movie films or similar transparencies to digital form. The proposed technique can perform the conversion 60 to 120 times faster than current techniques.
2. Description of the Related Art
Currently, high quality conversion systems convert film image frames to digital by moving the film by a linear array of photodetectors. A line of picture elements on the film image is imaged onto the array of photodetectors. In most cases, this line corresponds to a horizontal line on the film image. The lines are captured for conversion to digital by either strobing the illumination source or employing a line transfer technique on the photodetector array. The individual picture elements are then analog-to-digital (ADC) converted and stored on a digital medium. Three linear photodetector arrays are employed, one for each color axis.
It can be seen that the sequence of line captures will create a frame capture once all of the individual line outputs are assembled. Thus, it can be seen that the required two axes of scan are performed with one being the linear array and the other the film motion. The horizontal accuracy is determined by the photolithographic accuracy of the semiconductor process that created the linear array and is very accurate. The vertical accuracy is determined primarily by the accuracy with which the film is moved (an alternative is to move the photodetector array, but the future trend is to move the film). In either case, the motion control is the accuracy limiting element and the cost driving part of the system.
Unwanted side-to-side motion of the film degrades accuracy and subsequent ability to compress the digital movie is impaired because individual rows are misregistered. Also, the speed of conversion is severely limited. Current state of the art is 5 seconds per frame, or 1/120 of real time at 24 frames per second.
An alternative technique is to utilize a two dimensional array of photodetectors. This solves the accuracy problem for the array of picture elements and is potentially faster.
The current approach is to utilize a two dimensional array with a single serial pixel output because the CCD arrays are the same as those used in video camers and camcorders and these need a single video output. Commercial hardware with this approach still requires 5 seconds per frame. This will never approach the speeds necessary for commercial digital cinema.